Process for imparting wrinkle resistance and recovery properties to cotton stretch fabrics



"United States Patent Oifice 3,542,503 Patented Nov. 24, 1970 U.S. Cl.8116.3 6 Claims ABSTRACT OF THE DISCLOSURE The process of this inventioncomprises the steps of treating cellulosic material with aqueous alkaliand subsequently reacting the alkali treated material with an alkalicatalyzed resin or crosslinking agent.

An non-exclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government, with the power to grant sublicenses for suchpurposes, is hereby granted to the Government of the United States ofAmerica.

This invention relates to a continuous process for the production ofcellulosic textile materials having excellent stretch and wet-and-drywrinkle recovery properties. More specifically, it deals with acontinuous process comprising shrinking cellulosic fibrous textilematerials with an alkaline solution, and subsequently without tensionreacting the alkali-treated cellulose formed during the shrinkingprocess with a thermosetting resin or (other) suitable crosslinkingagent which may be catalyzed by the alkaline reagent.

The term cellulosic textile material or cellulosic fibrous materials, asused herein, relates to the natural cellulosic products such as cotton,linen, ramie, etc.; it also relates to the synthetic cellulosic fiberssuch as rayon, and the like. These products may be in the natural state,but better treatment is effected when the cellulosic material has beenprepared by conventional procedures for removing natural waxes, andother noncellulosic impurities. The fibrous materials may be in the formof yarns; or they may be knitted or woven fabrics.

Processes for producing stretch cottons by slack mercerization or otheralkali-contraction techniques are known in the art. Processes for thecrosslinking, or chemical treatment of cotton using alkaline catalystsalso are known. However, in the present-day art of producingwrinkle-resistant, cotton stretch-fabrics, each of the two processes iscarried out as a separate entity; this is frequently referred to as atwo-stage process. That is, the fabric is first slack mercerized, thenwashed completely free of alkali (or soured and rinsed) and dried. Thisis the first stage. The dry slack-mercerized cellulosic material is thenchemically treated by resination, or crosslinking, in the second-stagetreatment. Frequently, the equipment for these two stages of treatmentare at separate places in the plant, or the slack-mercerized cellulosicmaterial may be transported to another plant for the cross? linkingtreatment. In either case, since the chemical used for slackmercerization is completely removed from the cellulosic material in thefirst stage, additional caustic solution must be used when analkali-type catalyst is to be used in the second stage. US. Pat.3,145,132 teaches such a two-step batch finishing treatment in whichcomplete removal of the reagent that effects shrinkage of the cellulosicfibers is required, followed by drying before the crosslinking reactant,or thermosetting resin can be applied to the cellulosic material.

It is an object of this invention to provide a process wherebycellulosic textile materials may be treated so as to produce excellentstretch properties and a high level of wet-and-dry wrinkle resistance ina continuous sequence of finishing steps.

It is a further object of this invention to eliminate certain stepswhich are necessary in the above-mentioned two-stage batch process forproducing wrinkle-resistant, cotton stretch fabrics, thereby providingadded economy of time and expense.

These objects of our invention are accomplished by processing woven orknit cellulosic fabrics as follows:

(a) Impregnating the cellulosic fa bric under minimum tension with anaqueous solution of an alkaline swelling agent to shrink or reduce thedimensions of the material in one, or both, direction; this makes thefabric stretchable;

(b) Maintaining a period of dwell from about 0.5 to 5.0 minutes in thealkaline solution to insure uniform swelling and shrinking of thefabric;

(0) Removing the excess alkaline solution by mechanical means such aspadder rolls (squeeze rolls), centrifugation, and the like;

(d) Further increasing the swelling and shrinking of the fabric byreducing the concentration of the alkaline solution by rinsing in waterand passing through padder rolls (squeeze rolls) to give about 0.1 to 10weight percent residual alkali on the weight of the dry fabric;

(e) With minimum tension, passing the swollen, wet fabric of step (d)into, and through, a 2 to 20 weight percent solution of a crosslinkingreagent whose reaction with the cellulose is catalyzed by the residual(0.1 to 10%) alkaline reagent;

(f) With minimum tension, reacting the crosslinking agent with thecellulose (curing);

(g) With minimum tension, washing the crosslinked fibrous material toremove all unreacted chemicals and unwanted byproducts; and thereafter(h) Drying with minimum tension the cellulosic fabrics having excellentstretch properties and improved wet-and-dry wrinkle resistance.

This sequence of steps permits continuous processing of the fabric,eliminates costly washing, souring (acid treatment), rinsing, and dryingafter the alkali-shrinking step. It also permits utilization of thealkali-swelling agent as a catalyst during the resin-finishing, orcrosslinking step. The economy of this reduction in processing steps isapparent.

Two essential concentrations of the alkaline reagent are required inthis invention. In the first place, a concentration capable of shrinkingthe cellulosic material must be employed in step (a) above. For example,when a sodium hydroxide solution is used, a concentration of at least 13weight percent on the weight of the solution (OWS) at 32 F. is required.At ambient room temperatures (about to 86 P.) concentrations rangingfrom 3 about 23 to 30 weight percent (OWS) cause satisfactory shrinkageto be obtained.

For effective catalysts of certain reagents in the crosslinking step(step (f) above), a lower concentration of alkali is essential. Withsodium hydroxide at ambient room temperatures (65 to 86 F.) 0.1 toweight percent, on the weight of the fiber (OWF), is suitable forcatalyzing the reaction between the cellulose and the thermosettingresin, or crosslinking agent. Step ((1) above is achieved (without anintermediate drying step) by rising, and by adjusting the retention ofwater and alkali on, and in, the fabric. This may be done by squeezing(between padder rolls), centrifuging, or other available mechanicalmeans.

We have found that, when a fabric is impregnated with a sodium hydroxidesolution of about 23 weight percent at ambient temperatures (65 to 86F.), soaking for about 5 minutes in -50 times the weight of the dryfabric in water reduces the amount of residual sodium hydroxide to about4 to 8 weight percent alkali (OWF).

It is an advantage of the process of our invention that the applicationof sodium hydroxide solution of mercerizing strength to cotton materialfollowed by rinsing, and washing to about 4 to 8 weight percentconcentration (OWF) has the distinct advantage of producing a higherdegree of swelling of the cellulose with resultant improvement inshrinkage than is obtained from caustic solutions containing at least 13weight percent sodium hydroxide (OWS), at 32 F., or 23 to 30 weightpercent sodium hydroxide (OWS) at ambient room temperatures. Thisunexpected phenomenon was discovered by determination of the water ofimbibition which is recognized as an index of the state of swelling ofthe fibers. For example, the water of imbibition of a sample of cottonyarn treated by impregnation with 30 weight percent sodium hydroxide(OWS) was 105%. Portions of this yarn which had been impregnated with 30weight percent sodium hydroxide (OWS), and then reduced to 4 to 8percent sodium hydroxide (OWF) by rinsing and washing, hadwater-of-imbibition values of 122125%. (Water of imbibition was measuredby the weight of water retained by the fiber after centrifugation at1,000 times the force of gravity for minutes. The weight percent ofpickup of water is based on the original weight of the dry cotton.)These higher water-of-imbibition values indicate correspondingly greaterdegrees of swelling. Swelling and shrinkage are, of course, directlyrelated.

Alkaline swelling agents which may be used in the fabric contractionstep include sodium hydroxide, potassium hydroxide, trimethyl benzylammonium hydroxide, and the like. Concentrations sufiicient to bringabout mercerization and attendant shrinkage of the cellulose are used.In general, concentrations above about 13 Weight percent (OWS) arerequired. However, as noted above, the concentration of the shrinking(mercerizing) reagent is related to the temperature of the solution andmay vary from about 13 to 30 weight percent (OWS).

The fabric-contraction step is carried out at a temperature of about to86 F. or below, and for a time sufiicient to allow shrinkage to anextent which imparts stretchability to the fabric to occur. About 0.5 to5.0 minutes at ambient room temperatures is a good practice.

After the fabric has shrunk, it is treated with an amount of water suchthat upon adjustment of pickup, preferably 90 to weight percent (OWF)the concentration of alakli calculated as solids remaining, is about 0.1to 10 weight percent of the dry fabric. As noted above, residual alkaliserves as a catalyst in the subsequent chemical reaction step.

A thermosetting resin, usually amide-formaldehyde condensates, such asmethylolated urea, melamine, or other crosslinking reactants such asbis(Z-hydroxyethyl) sulfone, epichlorohydrin, dichloropropanol, thedisodium salt of tris(sulfatoethyl)sulfonium inner salt, and the like,whose reaction with cellulose is catalyzed by alkaline agents, is thenapplied. Application of the resin, or reactant, to the fabric wet withalkali solution may be by dipping, soaking, padding, spraying, brushing,and the like. However, for continuous operation a pad box equipped withone or more pairs of squeeze (padder) rolls is a good practice. Thefabric is passed into, and through, the alkaline solution prior topassage through the squeeze rolls. Concentrations of resin, orcrosslinking reactant, ranging from about 2 to 20 weight percent (OWS)may be employed. When the pickup is properly adjusted, the treatedfabric should also contain about 2 to 20 weight percent solid reagent(OWF). If one passage of the fabric into, and through, the crosslinkingsolution does not deposit the desired 2 to 20 weight percent solids onthe fabric, the fabric is passed through again until the desired amountis deposited on the fabric. Extreme care must be maintained to reducethe tension on the fabric at all times to a minimum to obtain the bestresults.

After application of the resin, or crosslinking reactant, to thealkali-containing fabric, reaction with the cellulose is allowed toproceed. This reaction may be carried out under (1) dry-cure conditions,or (2) in the wet state.

In a dry-cure reaction, the fabric may be dried and cured in a singleheat-treatment operation; or alterna tively it may be dried at atemperature sufficient to reduce its moisture content to about 10 weightpercent (OWF), or less, and subsequently heat-treated at a highertemperature to bring about a reaction between the cellulose and thecrosslinking agent. In this latter case, a delay period as much as sixmonths, or more, between drying and curing can be used, if desired.Preferred practical conditions for curing are about one minute to about10 minutes at temperatures from about 275 F. to about 365 F., the timeand temperature of curing being inversely related. Heavier-weightfabrics require stronger curing conditions, that is, the highertemperatures and/ or longer times than the lighter fabrics.

When curing is to be accomplished in the wet state, and the reagent isapplied to the alkali-containing fabric, the fabric is first rolled ontoa tube, or core; it is then wrapped in a plastic sheeting to preventevaporation of water, and allowed to stand at ambient room temperatureor at elevated temperature for a period of time. The time necessary forcompletion of the reaction may vary from a few minutes to several hours.Usually a standing time of about 30 to minutes at 77 to 95 F. causessatisfactory curing to be obtained.

After the reaction between the cellulose and the reagent is completed,the fabric is thoroughly washed, or soured and washed, to remove allunused reactant, catalyst, and/or byproducts. During all the handlingand final drying, it is essential that the fabric be processed withminimum tension to preserve the stretchability imparted by the shrinkingor swelling treatment.

When treated by the process of this invention, cotton fabrics havingexcellent stretch properties and wet-anddry wrinkle resistance areobtained. The values of these improved properties in a woven or knittedfabric are obvious to those skilled in the art of textile finishing.Furthermore, their values are indicated by the continuing, increasingdemands of the consumer for garments and other household items havingboth stretch properties, and wet-and-dry wrinkle resistance. Theseproperties when imparted to cellulosic textile products, provide greatercomfort and convenience to the consumer and at the present time are ingreat demand by the public.

The following examples are given to illustrate the invention and in noway are to be construed as restricting the obvious variations that maybe used to achieve similar results. Percentages are listed by weight onthe weight of the solution (OWS) or by weight on the weight of the dryfabric (OWF). The percentage of water of imbibition, although not sostated, relates to weight percent on the weight of the dry fabric.Sulfur is determined as described by I. Lysyj and J. E. Zarembo,Microchem. 1., 3, 173-80 (1959). Solubility is qualitatively observedmicroscopically by treating fibers from the sample with 0.5 Mconcentration of cupriethylenediamine solution. This test is. recognizedby those skilled in the art as a means of observing crosslinking and isdescribed by Tripp et al. in Textile Research 1., 31, 295-301 1961Nitrogen content is determined by the Kjeldahl method. Dry Wrinklerecovery angles are determined by the Monsanto method, ASTM designationD1295-53T. Wet wrinkle recovery angles were determined by soaking thespecimens 5 minutes at 150 F. in water containing 0.1% wetting agent,removing excess moisture by touching the edge of the specimens to ablotter, and then following the Monsanto procedure for dry recovery.

EXAMPLE 1 (1) A portion of desized, scoured, and bleached 80 x 80 wovencotton fabric measuring 9 inches by 9 inches, was marked into 9 squares,each 3 X 3 inches. From another portion of the same fabric 12 similar 3X 3 in. squares were marked, cut, and weighed, and the average dryweight of each square calculated. A 9 X 9 in. portion was then soaked inan alkaline solution containing 23 weight percent sodium hydroxide for 5minutes at ambient room temperature with no tension on the fabric. Thesample was then passed through a pair of squeeze rolls to give a pickupof about 90 to 110 weight percent (OWF). One marked square was cut off,placed in 100 milliliters of distilled water containing aphenolphthalein indicator and titrated with'standard l N HCl todetermine the amount of residual alkali in the fabric. The remainder ofthe original 9 X 9 in. sample was soaked in a volume of Water equal to50* times its dry weight for 5 minutes, then squeezed through pad rollsafter which another marked square was out 01f, and titrated to determinethe amount of residual alkali in the fabric.

The remaining portions of the original 9 x 9 inch sample were againsoaked in water equal in volume to 50 times their dry weight and thesame sequence, described above. was followed until titration showed noresidual alkali remained in the fabric. The data in the following'tableillustrate the amount of residue] alkali in the fabric after each stepoutlined above.

Weight percent No. rinses: NaOH in fabric 43.6

It will be observed that one rinse in an amount of water equal to about30 to 50 times the dry weight of the fabric before shrinking, followedby squeezing to about 90 to 110% pickup, reduces the strength of thealkali to about 4 weight percent alkali (OWF).

(2) A sample A of the same cotton printcloth used above was immersedtensionless in 23% sodium hydroxide solution at ambient roomtemperatureto effect shrinkage, and thus impart stretchability, then passed throughsqueeze rolls, rinsed in a volume of water equal to 50 times its dryweight for 5 minutes, and again squeezed. Concentrations of sodiumhydroxide remaining in the fabric Was about 4% of the weight of thefabric. This sample was then passed into, and through, an aqueoussolution containing Weight percent (OWS) of bis(2- hydroxyethyl)sulfone, passed through squeeze rolls again, dried 7 minutes at 140 F.,cured 3 minutes at 320 F., Washed thoroughly to remove unwantedchemicals, and dried.

(3) A second sample B was treated with 10 weight percent bis(2hydroxyethyl) sulfone as in (A) above after first being similarlyimmersed in 23% sodium hydroxide but rinsed twice with 50 times itsweight in water.

-(4) A third sample C was treated with 23% sodium hydroxide and rinsedfree of alkali. This sample was not Wrinkle recovery angles in degreesSulfur Solubility in warp plus fill content 0.5M weight, cupriethylenc-Sample Dry Wet percent diamine solution 231 257 0.75 Completelyinsoluble.

217 233 0.10 Partly soluble.

190 196 0.00 Soluble.

EXAMPLE 2 The procedures of Example 1 for samples A and B were repeatedexcept that a concentration of 20% bis(2- hydroxyethyl)sulfone (OWS) wasused. These samples are D and E, and correspond to A and B, respectivelyand had excellent stretch properties.

Wet wrinkle recovery angles (deg) Sulfur content weight, percent EXAMPLE3 The procedures for samples A and B of Example 1 were repeated exceptthe 10 weight percent solution of bis(2- hydroxyethyl)sulfone wasapplied to the samples by means of spraying. These samples are P and Gcorresponding to A and B, respectively and had excellent stretchproperties.

Wrinkle recovery angles in degrees Sulfur warp plus fill content weight,Dry Wet percent EXAMPLE 4 The procedure of Example 3 was repeated exceptthe concentration of bis(2 hydroxyethyl)sulfone was raised to 20%. Thesesamples are H and I corresponding to F and G, respectively and hadexcellent stretch properties.

Wet Wrinkle recovery Surface content angles (deg) Weight, percent SampleH 253 0. 73 I 240 0. 58 Control 196 0. 0

EXAMPLE 5 (A) A portion of a sample of cotton printcloth was soaked in25 weight percent sodium hydroxide solution without tension and allowedto shrink. It was then passed through squeeze rolls, rinsed with avolume of water equal to times its dry weight to give a sodium hydroxidecontent of about 4 weight percent (OWF), squeezed, and then passed into,and through, a solution containing 10% dimethylol urea. It was againpassed through squeeze rolls, passed into, and through, the 10% solutionof dimethylol urea a second time, and again passed through squeezerolls. It was then dried Without tension at F. for 7 minutes, and drycured at 320 F. for 3 minutes, after which it was thoroughly washed, anddried.

(B) Another portion of the same sample of cotton printcloth used in Aabove was treated as in part (A) of this example except that it wasrinsed twice with water after the shrinkage treatment, to give a sodiumhydroxide content of about 0.1 weight percent (OWF), and 20% dimethylolurea solution was used for the crosslinking treatment. It was thendried, cured, washed thoroughly, and again dried as in (A) above.

(C) A sample of cotton printcloth was soaked in 25% sodium hydroxidesolution and allowed to shrink. It was Washed free of alkali, and dried.

All fabrics had excellent stretch properties.

Results of these treatments are shown as follows:

Wrinkle recovery angles in degrew Nitrogen Solubility Warp plus fillcontent in 0.5 M

weight, cupriethylene- Dry Wet percent diamino solution 258 250 1. 6Insoluble. 273 258 2. 9 D0. 171 233 Soluble.

EXAMPLE 6 A portion of the same sample of cotton printcloth was soakedin 25 sodium hydroxide solution, squeezed, rinsed in 50 times its dryweight of water, passed through pad rolls, soaked in a 10 weight percentsolution of the disodium salt of tris(sulfatoethyl)sulfonium inner salt,passed through squeeze rolls to remove excess solution, rolled on aglass tube, and wrapped with an impermeable plastic film. It was allowedto react in this wet state at 80 F. for one hour, then washed free ofunused reactants and byproducts, and dried. The fabric contained 0.47%sulfur and was crosslinked, as is shown by its insolubility in 0.5 Mcupriethylenediamine solution and had excellent stretch properties.

EXAMPLE 7 Another portion of the same cotton printcloth used in Example6 was treated as in Example 6, except only bis(2 hydroxyethyDsulfone wasused. The treated fabric contained 0.11% sulfur, was insoluble incupriethylenediamine solution, and had excellent stretch properties.

We claim:

1. A continuous process for imparting excellent stretch properties andwet-and-dry wrinkle resistance to a cellulosic fabric selected from thegroup consisting of a woven cellulosic fabric and a knitted cellulosicfabric, comprising:

(a) impregnating the cellulosic fabric under minimum tension with anaqueous solution of an alkaline swelling agent selected from the groupconsisting of sodium hydroxide, potassium hydroxide, and trimethylbenzyl ammonium hydroxide, said solution 8 having a concentrationranging from about 13 percent at 32 F. to 30 weight percent at 86 F.;

(b) maintaining a period of dwell from about 0.5 to 5.0 minutes in thealkaline solution to reduce the dimensions of the fabric by shrinking;

(c) reducing the concentration of alkali in the impregnated fabric byrinsing the fabric in water and passing the rinsed fabric throughsqueeze rolls until the residual alkali concentration within the fabricis within the range of 0.1 to 10 weight percent based on the weight ofthe original dry fabric;

(d) with minimum tension, passing the resulting swollen, wet fabric ofstep (c) into and through a 2 to 20 weight percent solution of acrosslinking reagent whose reaction with the swollen cellulose iscatalyzed by the residual alkaline agent;

(e) with minimum tension, reacting the crosslinking agent with thecellulose;

(f) with minimum tension, washing the crosslinked fabric to remove allunreacted chemicals and unwanted byproducts; and thereafter (g) withminimum tension drying the fabric having excellent stretch propertiesand wet-and-dry wrinkle resistance.

2. The process defined in claim 1 wherein the wet fabric of step (d) isdried and subsequently cured with minimum tension at an elevatedtemperature ranging from about 275 to 365 F. for about 1 to 10 minutes,the higher temperature requiring the shorter curing time.

3. The process defined in claim 1 wherein the wet fabric of step (d) iscured without tension at ambient room temperature for about 30 tominutes prior to washing and drying.

4. The process defined in claim 1 wherein the alkaline swelling agent issodium hydroxide.

5. The process defined in claim 1 wherein the crosslinking agent isselected from the group consisting of dimethylol urea, methylolatedmelamine, bis(2-hydroxyethyl)sulfone, epichlorhydrin, dichloropropanol,and the disodium salt of tris(sulfatoethyl)sulfonium inner salt.

6. The process defined in claim 2 wherein the wet fabric is dried to amoisture content not greater than 10 weight percent and the heattreatment has a delay period not greater than six months.

References Cited UNITED STATES PATENTS 2,950,553 8/1960 Hurwitz 8l16.3 X3,145,132 8/1964 Seltzer 2874 X 3,285,690 11/1966 Cooper et a1. 8116.3

OTHER REFERENCES Gardon: A Quantitative Study of Crosslinking CottonWith N-Methylol Acrylamide, Journal of Applied Polymer Science, vol. V,issue 18, pp. 734-739.

Ward: Chemistry and Chemical Technology of Cotton, IntersciencePublishers, Inc., New York, 1955, p. 507.

LEON D. ROSDOL, Primary Examiner M. HALPERN, Assistant Examiner US. Cl.X.R. 8-116,

